11_immutable.cf: Make sure to clean up all immutable files

Failing to do so will cause the build to fail later on.

```
13:16:26 rsync: [generator] delete_file: unlink(tmp/12_immutable.txt.nuked) failed: Operation not permitted (1)
```

Ticket: ENT-10961, CFE-1840
Signed-off-by: Lars Erik Wik <lars.erik.wik@northern.tech>

Author: larsewi

tests/acceptance/10_files/unsafe/11_immutable.cf

@@ -87,14 +87,19 @@ bundle agent destroy
   commands:
     "chattr -i $(global.testfile)"
       contain => in_shell,
-      handle => "is mutable",
+      handle => "is mutable 1",
+      if => fileexists("$(global.testfile)");
+    "chattr -i $(global.testfile).gz"
+      contain => in_shell,
+      handle => "is mutable 2",
       if => fileexists("$(global.testfile)");
 
   files:
     "$(global.testfile)"
       delete => tidy,
-      depends_on => { "is mutable" };
+      depends_on => { "is mutable 1" };
   files:
     "$(global.testfile).gz"
-      delete => tidy;
+      delete => tidy,
+      depends_on => { "is mutable 2" };
 }